There is a mystery in Hong Kong: Why is roadside air quality so bad? The government has put in place various initiatives over the years to require new vehicles to comply with the latest standards, and to require the use of cleaner fuels.

According to models, there should have been solid improvements. Yet, roadside monitoring stations show daily emissions levels that are very high and harmful to public health.

The problem is most likely the models! They are only as good as the assumptions and in-put used. It is highly likely that the in-puts are wrong. The actual emissions from the Hong Kong vehicular fleets are probably much worse than estimated.

There is a lesson here for other cities from Hong Kong’s experience. While Hong Kong is said to have a developed economy with good regulatory systems on the whole, its vehicular emissions regulation has fallen behind.

Officials haven’t had the courage to take the oldest vehicles off the road, and they haven’t put in place tough vehicle inspection and maintenance system to ensure those that are on the road are properly maintained so as to minimize pollution.

Inspection and maintenance of vehicles is one of those subjects people talk little about but it is an important issue all governments must focus on.

It’s easy for people to buy vehicles – you just need to have the money to do so. It’s harder for people to learn how to drive them properly. Bad driving habits will degrade the engine quicker, waste fuel and may even be a road safety risk.

Even harder is to learn how to maintain a vehicle so it is properly tuned for safety and environmental reasons. An individual driver is unlikely to learn about vehicle maintenance – we just want to take it somewhere for a check-up periodically and have a vehicular mechanic industry that can fix problems.

The problems have to be properly identified – and this is the job of the authorities to create an inspection and maintenance system that can provide the information about the health vehicles.

The difference in emissions between a well-maintained vehicle and a poorly-maintained one is enormous. Hong Kong’s environmental protection agency states the difference could be more than four times. In fact, the difference may be even greater.

Studies in the US show an entire fleet of badly-maintained vehicles could emit as much as 20 times that of a well-maintained fleet. With new engine and fuel technologies, the low emitters are much cleaner than they used to be while the high emitters are just as bad.

Research is clear that the absolute emissions differences between well- and badly-maintained vehicles of any age (i.e. even older vehicles) are considerable larger than the age of vehicles. This can be seen from records in Los Angeles, where 20 percent of the worst maintained vehicles account for the vast majority of the tailpipe emissions.

To collect accurate vehicular emissions data, governments have to be prepared to carry out random emissions tests to assess what is the pollution contribution from poorly maintained vehicles. Poor maintenance includes deliberate tampering with or removal of pollution controls (particularly catalysts) and mis-fueling (using lower quality fuels than recommended).

Hong Kong’s roadside mystery can be solved by checking actual emissions and then run the model with more accurate information. Cities less advanced than Hong Kong are likely to also have poor inspection and maintenance systems. They should bear in mind that as their vehicle fleets grow, they must not overlook to put a good system in place so as to protect public health for their residents.

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